Kinda like if someone argued that Japan wasn't a major naval power in 1922 because most of their major warships had been built in Britain... and that the few that had been built in Japan used either British-built boilers, turbines, & guns or Japanese built ones which were slight modifications of British designs.
The Washington Naval Treaty of 1922 acknowledged Japan as the 3rd-most-powerful navy (after the US & Britain, but ahead of France and Italy).
Exactly right - the Japanese sent people to study engine designs in Great Britain, guns and armored steel in Germany, and ship design in France. Then they went home, and didn't just copy the designs they studied them and improved them all to make their own ships - better shells and ways to improve the pressures the guns could fire at, more efficient reciprocating engines, and better armor plating techniques that left less room for critical fractures on impact. Then they went out and virtually annihilated one of the most powerful and advanced fleets in the world at the time in 1905 - including one of the most advanced protected cruisers made -the Varyag - that had been built in the US for the Russians!
In fact, the Knyaz Suvorov, flagship of the Russian fleet, was built to French specifications but since it didn't have the Japanese's improvements Togo's ship, the Mikasa blew it to pieces in record time; she was hit so hard and so fast by the improved Japanese guns and shells that her plating actually began to burn in places and one of her turrets was sent flying.
I see the Aslan as having done the same thing without firing a shot to do it - they had something advanced fall into their laps and they studied it, improved it (since they aren't stuck at the same jump number), and produced enough of them to build a fleet. And from what little I know of the Aslan they weren't exactly neobarbarians when the first jump drive was found by them.
I'd argue a better way to determine an race's status is how technologically advanced they are regardless of jump drive discovery. Once you seem to hit the key prerequisites of fusion power (or similar), computer capability to control a jump, and master gravitics for building acceleration buffers and drives then the jump drive is as good as done.
Unless....and here I find another problem with this Major Race concept: what if you are just unlucky enough to have insufficient access to the lanthanides needed to make a jump drive but have everything else? Or are even more advanced - like distingrators, teleportation, AI computers, etc..that are listed as above Imperial standard TL? What are you then, just enlightened Minor Races?